Abnormal B cell lines from patients with agammaglobulinemia have been established and the molecular basis for their abnormality is under investigation. Probes for human Ig heavy chain mRNA are being used to study these abnormal B cells. The cellular basis of immunoregulatory defects is being investigated with T3, T4, T5, T6, T8 and T10 antibodies to determine T cell subset abnormalities in graft-versus-host disease, atopic dermatitis, hyper IgE syndrome, in addition to the whole panoply of immunodeficiency disorders. Lysis of subsets with complement-fixing monoclonal antibodies will provide clues to the correction of in vitro defects by parental or histoidentical sibling mononuclear cells.